Pharmacology and Pharmacotherapeutics
Core concepts
You must link drug mechanism to clinical effect. Know receptor families (ligand-gated channels, G-protein coupled, kinase-linked, nuclear), agonist/antagonist/inverse agonist concepts, and dose–response relationships (potency vs efficacy, ED50, therapeutic index). Understand pharmacokinetic parameters - volume of distribution, clearance, half-life, bioavailability - and how they change in renal or hepatic impairment. Know autonomic pharmacology (sympathetic and parasympathetic transmitters and receptors), and the mechanisms of major drug classes: antihypertensives, antidiabetics, antibiotics, anticoagulants, analgesics, and psychotropics. Drug–drug interactions arising from enzyme induction/inhibition (CYP450) and transporter effects are common exam material.
Traps in questions
- Confusing potency (dose needed) with efficacy (maximum effect).
- Assuming a longer half-life means a stronger drug.
- Forgetting that enzyme inducers lower plasma levels of co-administered substrates.
- Mixing up competitive (surmountable) and non-competitive (insurmountable) antagonism.
Worked example / rule of thumb
A drug has a half-life of 8 hours. Steady state is reached in roughly 4–5 half-lives, so about 32–40 hours. Rule of thumb: loading dose = (Vd × target concentration)/bioavailability; maintenance dose rate = clearance × target concentration. For interactions, remember induction takes days to weeks (new enzyme synthesis) while inhibition is immediate.